The present invention relates to engine starters for internal combustion engines and, more particularly, to starters of the positive shift type wherein, after the starter motor pinion engages the flywheel gear of the engine to be started, the coaxial solenoid prevents the pinion gear from de-meshing until the starter motor is de-energized. The present invention represents an improvement over the engine starter drive taught in U.S. Pat. No. 4,366,385 issued Dec. 28, 1982, to Williams, owned by the assignee of the present application, the specification of which is hereby incorporated by reference.
Starter motors of the type having a shifting solenoid mounted on the outside of the starter motor housing have been used extensively in automotive and allied industries for starting internal combustion engines. However, in present industrial and automotive applications, this type of starter motor, often referred to as the "piggyback solenoid engine-starter", is not completely satisfactory because of the space that the piggyback solenoid occupies. Furthermore, it is desirable, from a production standpoint, to produce a starter housing that is easily adaptable to the various mounting positions required to satisfy a number of engine configurations. By eliminating the piggyback solenoid from the outside of the starter motor housing, the starter motor housing may be mounted in any desirable orientation on the engine without special consideration being given to the shifting solenoid or related parts. In addition, the starter motor can be manufactured to satisfy the various mounting requirements for various types of internal combustion engines, thereby limiting the need of manufacturing several types of starter motor housings.
Coaxial solenoid type starter motors, which eliminate the need for piggyback solenoids, have been known in the prior art. For example, Mattson, U.S. Pat. No. 3,084,561, uses a movable solenoid and helical splines to move the pinion and overrunning clutch prior to closing the motor power switch to rotate the armature.
Giometti, U.S. Pat. No. 3,572,133, has a friction connection between the shiftable drive portion and the starter motor housing for assisting the advance of the shiftable drive portion into engagement with the ring gear. An electromagnetic brake is also provided in order to prevent drive rotation and to facilitate drive advance into engagement with the ring gear. As the pinion drive engages the ring gear, the electromagnetic brake is de-energized.
Seilly U.S. Pat. No. 2,727,158, uses a solenoid to move the shiftable drive portion axially to initially engage the engine ring gear. As this occurs, a switch closes the contact to pass current through the motor to rotate the starter shaft. This causes the shiftable drive portion to further slide axially into full engagement with the ring gear. A catch ball arrangement is provided to secure the shiftable drive portion to the sleeve, which then de-energizes the solenoid.
In U.S. Pat. No. 3,124,694, Seilly provides an axially movable core to impart initial axial movement to the shiftable drive portion.
U.S. Pat. No. 3,922,558, to Hollyoak, provides an electromagnetic arrangement for moving the pinion assembly from its rest position to its operative position. In this drive connection, there is a member which bears against one end of the pinion assembly between the electromagnetic arrangement and the pinion assembly. This member, in the rest position of the pinion assembly, is trapped between the pinion assembly and a collar carried by the shaft. When the electromagnet is energized, it moves the armature in such a manner that the pinion assembly is urged by way of the member toward its operative position. The shaft and the pinion assembly rotate relative to the armature and the member when the electric motor is energized. However, the armature and the member act as a brake to inhibit rotation of the pinion assembly and the shaft, when the pinion assembly returns to its rest position. In the rest position, the member is trapped between the pinion assembly and the collar carried by the shaft.
In Nardone, U.S. Pat. No. 1,939,405, and in Celio, U.S. Pat. No. 2,333,765, an electromagnet is used to cause axial movement of the drive portion into mesh with the flywheel prior to causing rotation of the starter motor shaft.
None of the above identified prior art starter motors has proven to be entirely satisfactory for present day use for various reasons. Some of these starters were unreliable in service over an extended period of time. Others were too expensive to manufacture. Many other problems were also presented in the production of coaxial types of starters such as the provision of suitable electric characteristics of the solenoid and accompanying parts, the provision of a suitable on/off switching for the electric starting motor, and the reduction of overall manufacturing costs. Furthermore, all of the above identified prior art designs utilize an electromagnetic coil which requires a relatively large current draw to facilitate engagement of the starter drive with the ring gear.
In Williams, U.S. Pat. No. 4,366,385, a first solution to the above described problems was offered. In Williams, the starter drive advances the drive pinion on helical splines without rotation, by inertia, to engage the engine ring gear. The drive pinion is held in engagement with the engine ring gear by an engaging mechanism which allows the total motor torque to be transmitted to the ring gear until the motor is de-energized. More particularly, Williams provides a starter drive for internal combustion engines having a starter drive housing, a motor driven shaft, a cylindrical end portion, and a helical threaded portion between the cylindrical end portion and the motor. The starter drive includes a screw sleeve mechanism for cooperatively engaging the helical threaded portion on the motor driven shaft. A ring armature member is centrally disposed relative to the screw sleeve mechanism and is connected to the screw sleeve mechanism. Furthermore, a drive pinion is coaxially disposed on the cylindrical end portion of the motor driven shaft. A unidirectional clutch mechanism interconnects the screw sleeve mechanism and the drive pinion. Finally, the ring armature mechanism is engaged to the starter drive housing when the drive pinion is advanced along the motor driven shaft by rotation of the motor when the motor is energized so as to engage the engine ring gear. Thus, the drive pinion is held in engagement with the engine ring gear and total motor torque is transmitted to the ring gear until the motor is de-energized.
While Williams represented a substantial improvement over the prior art engine starter drives, the deceleration peak torque of the engine starter drive disclosed therein was somewhat higher than what is desirable which, in some instances, leads to premature drive failure and excessive ring gear wear. Furthermore, assembly of this engine starter drive was expensive.
The present invention provides an engine starter drive similar to that taught by Williams, but having a more compact configuration reducing the number of parts, and a reduced deceleration peak torque, thus resulting in space savings, a lower cost of assembly, and the use of lower cost materials.